add xhr upload option, see pull request #206

Author: steffans

src/http/client/xhr.js

@@ -37,6 +37,10 @@ module.exports = function (request) {
             _.extend(xhr, request.xhr);
         }
 
+        if (_.isPlainObject(request.upload)) {
+            _.extend(xhr.upload, request.upload);
+        }
+
         _.each(request.headers || {}, function (value, header) {
             xhr.setRequestHeader(header, value);
         });

src/http/index.js

@@ -48,6 +48,7 @@ Http.options = {
     params: {},
     headers: {},
     xhr: null,
+    upload: null,
     jsonp: 'callback',
     beforeSend: null,
     crossOrigin: null,